1. Field of the Invention
The invention relates to an endless papermakers belt for paper machines or the like with a number of helices which consist of opposing winding legs and headcurves joining those legs together and into whose intermediary spaces the headcurves of the neighboring helix are entered to a degree such that there develops between the two helices a range of overlapping into which a rod or pintle is inserted.
2. Description of the Prior Art
Such belts are described, for example, in German Pat. No. 2,419,751 and in German Patent (Disclosure copy) No. 2,938,221. In both cases, the helices consist of wire usually with a round or slightly oval cross-section. Such wire belts exhibit an exceptionally high air permeability. In the manufacture of paper, this often leads to paper flutter.
In addition, there is the fact that usually only one so-called contact point occurs between these known belts and the paper web at the supporting winding legs. Depending on the weight and quality of the paper and the pressing pressure occurring during manufacture, this can lead to impressions of the winding legs being visible in the finished paper. To be sure, these impressions are desired, for example, in papers whose surface is supposed to exhibit a pattern; in the manufacture of high-quality smooth papers, in contrast, these impressions are to be avoided.
Also known are wire belts in which at least the web-supporting winding legs of the helices exhibit flat supporting surfaces. These flat supporting surfaces may be produced, for example, when flat wires or shaped monofilaments are used in manufacturing the helices. This has the disadvantage, however, that one must accept between neighboring winding legs a large air passage which is generally of the width of the flat wires or shaped monofilaments and which in many cases should be avoided. The prior art has attempted in complicated fashion to regulate the passage of air in such wire belts using various types of inserts within the helices. This, however, results in reduced mobility between neighboring helices of the belt, especially in turning around rolls. The introduction of the inserts is an intensive process and they can increase the weight of the belts very considerably.
Known finally are endless belts for paper machines in which at least the web-supporting winding legs of the helices exhibit flat supporting surfaces whose width is greater than the wire diameter or than the wire width of the headcurves (German Pat. No. 3,243,512).
By varying the width of the supporting surfaces of the helices, one can influence the passage of air through the wire belts over a broad range. In addition, there is the fact that the relatively wide supporting surfaces avoid pointwise contact between the belts and the paper web which is one difficulty with the prior art belts.
It has been found, however, in operating these wire belts that slight irregularities or roughenings in the supporting surfaces adversely affect the manufacture of high-quality papers in which even the slightest marking must be avoided.
It has already been proposed to needle such belts with a mat consisting of very many thin compacted textile filaments.
The difficult thing is to guarantee permanent consolidation of the mats on the wire belts. It has been found that, especially upon turning of the belts around rolls, relative movement occurs between the belt and the mat needled thereto, which, over the long term (especially at the high operating speeds of modern equipment) leads to a loosening of the mat from the belt over the course of time.
In addition, there is the fact that previously used mats have been relatively air-tight so that they permit influencing the flow of air through them only to a limited degree. A serious problem here is that, as a result of an abrasion of the mat and the paper web, a fine dust is formed which clogs the porous openings in the mat. The consequence of this is that the air permeability of such mat-needled endless belts descreases and finally becomes insufficient.